Enhanced release of striatal dopamine following medial hypothalamic damage in rats

Rats given bilateral lesions of the medial hypothalamus, using either direct or radio frequency current, and killed 2 hours later showed a significant elevation in striatal concentration of homovanillic acid (HVA), while striatal dopamine (DA) was unaltered. After unilateral damage the elevated HVA was seen only in the hemisphere ipsilateral to the lesion. In rats killed 2 days after such damage, the striatal HVA did not differ from controls. The elevation of HVA, suggesting an enhanced release of striatal DA, is associated with a resistance to the cataleptic action of the DA receptor blocking agent droperidol. The present findings suggest that medial hypothalamic lesions can increase neurotransmission within brain DA neurons, and that this neurochemical event may account for at least some of the short-term behavioral effects of these lesions. The relationship of these brain events to the long-term behavioral effects of the lesion remains an important issue for future research.     

Effects of long-term recovery from transient cerebral ischemia in rat brain: Tissue levels of acetylcholine,monoamines, and their metabolites

Concentrations of acetylcholine and the monoaminergic neurotransmitters dopamine, serotonin and their respective metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 4-hydroxy-3-methoxyphenylacetic acid (HVA), 5-hydroxyindolacetic acid (5-HIAA) and choline were simultaneously determined in the corpus striatum of rats after 15 min. complete cerebral ischemia (CCI) and in different intervals (1, 24, 48, 72, 96 hours) of postischemic cerebral reperfusion. Results were compared to respective sham-operated control animals. After 15 min. CCI acetylcholine concentration decreased to 15%, and dopamine concentration to 56% of the control values. The metabolite levels of DOPAC decreased to 40% and HVA to 64% of the control values. Acetylcholine, dopamine, serotonin and choline concentrations were not changed significantly after reperfusion. The metabolites HVA and 5-HIAA showed their maximum increases after 1 and 24 hours of reperfusion, additionally HVA was decreased both, after 72 and 96 hours of reperfusion. The data indicate that surprisingly little permanent damage could be caused by a 15 min. ischemia in the striatum. Tissue levels of the neurotransmitters appeared differentially altered but similarly regulated during ischemia and subsequent recirculation. Acetylcholine and dopamin levels decreased profoundly during ischemia. However, acetylcholine levels could be compensated rapidly during reperfusion, whereas the dopaminergic system showed a long-lasting change in its turnover rate. Although serotonin levels were unaffected by CCI, there was an increase of its presumed turnover rate during reperfusion.     

MK801 antagonism of the prolonged depletion of striatal dopamine by amphetamine in iprindole-treated rats.

The administration of amphetamine to rats pretreated with iprindole to inhibit the metabolism of amphetamine results in a long-lasting depletion of striatal dopamine and its metabolites, DOPAC and HVA. Pretreatment with MK801, a noncompetitive antagonist of the NMDA (N-methyl-D-aspartate) subclass of excitatory amino acid receptors, antagonized the depletion of striatal dopamine, DOPAC and HVA 3 days after a single dose of amphetamine in iprindole-treated rats. MK801 pretreatment was effective up to 4 hours but not at 8 or 24 hours in preventing amphetamine effects on striatal dopamine, DOPAC and HVA.     

Release of homovanillic acid from the brain of children.

Cerebral arterio-venous differences of homovanillic acid (HVA) and cerebral blood flow were measured in 24 patients, 6 adults and 18 children, anaesthetized by different techniques. A statistically significant release of HVA from the brain (p < 0.001) was demonstrated in five children anaesthetized by barbiturate, nitrous oxide and droperidol/fentanyl. The release rate was 509 pmoles HVA/100 g brain tissue/minute - corresponding to approximately 1.3 mg HVA/24 hours from the whole brain.     

Direct determination of homovanillic acid release from the human brain, an indicator of central dopaminergic activity

The plasma concentration of the dopamine (DA) metabolite, homovanillic acid (HVA), is used as an indicator of central nervous system dopaminergic activity. Using percutaneously inserted catheters we were able to obtain blood samples simultaneously from the right and left internal jugular veins. Veno-arterial HVA plasma concentration differences combined with adjusted organ plasma flows were used, according to the Fick Principle, to determine the HVA overflow from the brain. The HVA overflow from the liver was also measured. HVA overflow from the brain represented 12% of the total body HVA production. A similar amount was released from the liver, illustrating the limited validity of peripheral plasma HVA measurements as an indicator of central dopaminergic activity. HVA release from the human brain displayed a degree of asymmetry, the overflow into the left internal jugular vein being 36% greater than that into the right. Cerebral venous blood flow scans indicated that cortical cerebral regions drained preferentially into the right internal jugular; by inference the higher HVA overflow on the left originated from dopamine-rich subcortical brain areas. Since HVA in plasma may arise from the metabolism of DA existing either as a neurotransmitter or a norepinephrine (NE) precursor we measured the internal jugular vein plasma concentrations of NE, and its metabolite dihydroxyphenylglycol (DHPG), to determine whether they displayed a similar pattern of release to HVA. The overflow of both NE and DHPG into the right internal jugular vein was approximately double that on the left. Since the overflow of HVA did not parallel that of NE and DHPG it may be inferred that the origin of much of the subcortically produced HVA is from dopaminergic neurons and not from the metabolism of precursor DA in noradrenergic neurones or cerebrovascular sympathetic nerves.     

Determination of isomeric acid dopamine metabolites in human cerebrospinal fluid by mass fragmentography

A method for the quantitative determination of the isomers 4-hydroxy-3-methoxyphenylacetic acid (HVA) and 3-hydroxy-4-methoxyphenylacetic acid (iso-HVA) in cerebrospinal fluid (CSF) by mass fragmentography has been developed. The heptafluorobutyryl methyl ester derivations of the two compounds could not be separated by gas chromatography. The relative intensity of the base peak (m/e 333) and the molecular ion (m/e 392) in the mass spectra were, however, quite different and allowed a separate determination. Contradictory to a previous report, it was found that the concentration of iso-HVA was less than 2% of the HVA level in the investigated 12 CSF samples from patients with different diseases.     

The effect of frontal cortex lesion on the activity of the dopaminergic system in rat striatum

The experiment was carried out on male Wistar rats weighing 180-220 g with lesion in the cortex of the frontal lobe. The activity of the dopaminergic system was studied by means of behavioural tests such as determination of spontaneous motor activity, apomorphine-induced stereotypy, haloperidol-induced catalepsy. Increased intensity of stereotypy was observed reaching a maximum 14 days after frontal lobe damage. Moreover, a slight tendency was observed for inhibition of haloperidol-induced catalepsy without changes in the spontaneous motor activity of the animals. Biochemical investigations demonstrated reduced dopamine content in the striatum on the side of the lesion.     

Baclofen and γ-hydroxybutyrate: similar effects on cerebral dopamine neurones

Baclofen (20 mg/kg) caused an increase in the content of homovanillic acid (HVA) and dopamine (DA) in rat brain 2–3 h after drug injection without appreciable changes in the level of other monoamines and their main metabolites. Six and eight hours after baclofen, the content of HVA but not that of DA was reduced. Moreover, baclofen initially (20 min after injection) reduced, but later (105 min post drug) enhanced the accumulation of HVA induced by probenecid. The shortlasting (20 min) initial reduction of HVA elevation in probenecid-pretreated animals as well as the longlasting (6–8 h) decrease of HVA levels in rats injected with baclofen alone are interpreted to be due to a decreased release and metabolism of DA, probably as a consequence of the blockade of impulse flow in mesolimbic and nigro-striatal DA neurones. The increase in HVA and DA seen during the first few hours is thought to result from enhanced DA synthesis similar to that known for γ-hydroxybutyrate (GHB). This initial rise in HVA due to synthesis stimulation probably masked a reduction of HVA to be expected immediately after baclofen injection. The similarity between baclofen and GHB is stressed by the finding that baclofen counteracted the increase of HVA occuring after chlorpromazine and D-amphetamine but not that induced by the benzoquinolizine derivative, Ro 4-1284.     

Dopamine and its metabolites in human peripheral nerves: Is there a widely distributed system of peripheral dopaminergic nerves?

Norepinephrine (NE), dopamine (DA) and its metabolites homovanillic acid (HVA) and 3, 4-dihydroxyphenylacetic acid (DOPAC) were analyzed in human ventral spinal nerve roots and peripheral nerves by gas chromatography-mass spectrometry. High concentrations of DA and HVA were found in almost all tissues analyzed. The concentration of DA and HVA was usually higher than in blood. In vagus nerve and in some spinal nerve roots, the concentration of DA was higher than that of NE, while in other nerves (splanchnic nerve and genitofemoral nerve) DA represented 20 or more percent of NE. The concentration of HVA was usually higher than the concentration of DA indicating that a large portion of DA in peripheral nerves is catabolized and not converted to NE. High concentrations of DA and HVA in human peripheral nerves indicate that a wide distribution of peripheral DA-containing nerves might exist. The distribution of DA in different nerves suggests an association of potential DA-containing nerves with the autonomic nervous system.     

Group 3 LEA Gene HVA1 Regulation by Cold Acclimation and Deacclimation in Two Barley Cultivars with Varying Freeze Resistance

The level of expression of the group 3 late embryogenesis abundant abscisic acid-regulated gene (HVA1) to cold treatment has been studied in winter barley (Hordeum vulgare) seedling tissue. The cDNA clone (pHVA1) encoding this late embryogenesis abundant protein was used as a hybridization probe to detect the corresponding mRNA. Expression of the HVA1 gene was determined after the tissue had been subjected to a regimen of 2°C exposure (cold acclimation), followed by a return to 25°C growth conditions (deacclimation). Accumulation of HVA1 mRNA occurred upon cold acclimation of the tissue and disappeared as early as 2 hours after exposure to deacclimation conditions. A comparison of the response to cold acclimation and deacclimation was made between seedling tissue of a freeze-resistant and less freeze-resistant cultivar. In both cultivars, the HVA1 gene was expressed and modulated by cold treatment. Within 2 hours of deacclimation HVA1 mRNA was no longer detectable in either cultivar independently of freeze resistance. The level of expression of HVA1 appeared to be greater in the less freeze-resistant cultivar (Winter Malt).     

Conjugated 3,4 dihydroxy phenyl acetic acid (DOPAC) in human and monkey cerebrospinal fluid and rat brain and the effects of probenecid treatment

Gas chromatography-mass spectrometry (GC-MS) was used to measure 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in cerebrospinal fluid from humans and monkeys and in rat caudate nuclei. DOPAC was found to be present mainly in conjugated form. In human lumbar CSF the average concentration of total DOPAC before probenecid treatment was 1.48 ± 0.31 ng/ml; after probenecid it increased to 15.06 ± 3.17 ng/ml. This increase was mainly due to conjugated DOPAC but increases in free DOPAC also occurred. There is a relatively greater accumulation of DOPAC than of HVA, suggesting that in human CSF conjugated DOPAC may have a faster turnover rate than HVA. In monkey, ventricular CSF contained higher concentrations of DOPAC and HVA than did lumbar CSF.In rat brain, treatment with probenecid caused increases in DOPAC, HVA and their conjugates.These results suggest that DOPAC is conjugated in brain and that both compounds are removed from brain and CSF by a probenecid-sensitive acid transport system in the same manner as is HVA.     

The acute effects of central- and peripheral-acting dopamine antagonists on plasma HVA in schizophrenic patients

The short-term effects of fluphenazine on plasma HVA concentrations were compared with the effects of fluphenazine and concurrent administration of debrisoquin, a monoamine oxidase inhibitor which does not cross the blood brain barrier and is used to enhance the CNS contribution to circulating plasma HVA concentrations. Fluphenazine significantly increased plasma HVA with or without debrisoquin 24 hours following the initiation of treatment. Domperidone, a butyrophenone dopamine antagonist which acts only in the peripheral nervous system, failed to alter plasma HVA concentrations. These data suggest that the acute effects of neuroleptic drugs on plasma HVA concentrations are dependent upon interaction with CNS dopaminergic systems and provide additional support for the use of plasma HVA as a reflection of CNS dopamine system activity in clinical studies.     

Estrogen potentiates the stereotypy induced by dopamine agonists in the rat

Repeated weekly treatment with 100 μg/kg of estradiol benzoate (EB) to ovariectomized female rats intensified the stereotypy induced by the dopamine agonists amphetamine and apomorphine. A similar effect on amphetamine-stereotypy was produced 48 hours after a single injection of 10 μg/kg of EB. The fact that EB failed to increase blood or brain levels of either ³H-amphetamine or ³H-apomorphine suggests that these behavioral effects were not due to altered peripheral drug metabolism or uptake into the brain. The enhancement of stereotypy produced by EB is viewed as one manifestation of a more complex modulatory influence of estrogen on DA function.     

Differential regulation of low and high voltage-activated calcium channels in neonatal rat myocytes following chronic PKA modulation

The biophysical properties of voltage-dependent cardiac calcium channels (VDCC) can be modulated by protein kinases. In this study, we investigate whether long-term treatment with protein kinase A (PKA) modulators alters the VDCC activity in neonatal ventricular myocytes. Using whole-cell patch-clamp recordings, we found an increase in high-voltage activated (HVA) current density and a corresponding decrease in low-voltage activated (LVA) current density in neonatal rat ventricular myocytes up to 6 days in culture. Long-term exposure to 8Br-cAMP, a PKA stimulator, increased the HVA current density at 7 and 24 hours. In contrast, H89, a PKA inhibitor, caused a biphasic change in the HVA, an initial reduction at 7 hours exposure followed by an increase up to 4 days. In addition, H89 caused a sustained increase in LVA currents from 7 hours to 4 days. These findings suggest that chronic exposure to H89 changes LVA and HVA calcium current activities in cardiac myocytes. PKA is a key target of beta-adrenoceptor activiation, thus, our findings suggest long-term repeated use of beta-adrenergic drugs may induce unexpected functional alteration of VDCCs.     

Differential regulation of low and high voltage-activated calcium channels in neonatal rat myocytes following chronic PKA modulation

The biophysical properties of voltage-dependent cardiac calcium channels (VDCC) can be modulated by protein kinases. In this study, we investigate whether long-term treatment with protein kinase A (PKA) modulators alters the VDCC activity in neonatal ventricular myocytes. Using whole-cell patch-clamp recordings, we found an increase in high-voltage activated (HVA) current density and a corresponding decrease in low-voltage activated (LVA) current density in neonatal rat ventricular myocytes up to 6 days in culture. Long-term exposure to 8Br-cAMP, a PKA stimulator, increased the HVA current density at 7 and 24 hours. In contrast, H89, a PKA inhibitor, caused a biphasic change in the HVA, an initial reduction at 7 hours exposure followed by an increase up to 4 days. In addition, H89 caused a sustained increase in LVA currents from 7 hours to 4 days. These findings suggest that chronic exposure to H89 changes LVA and HVA calcium current activities in cardiac myocytes. PKA is a key target of β-adrenoceptor activiation, thus, our findings suggest long-term repeated use of β-adrenergic drugs may induce unexpected functional alteration of VDCCs.     

Rhythmic changes in metabolism of dopamine in the chick retina: the importance of light versus biological clock

Rhythmic changes in dopamine (DA) content and metabolism were studied in retinas of chicks that were adapted to three different lighting conditions: 12-h light : 12-h dark (LD), constant darkness (DD) and continuous light (LL). Retinas of chicks kept under LD conditions exhibited light-dark-dependent variations in the steady-state level of DA and the two metabolites of DA, i.e. 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA). Concentrations of DA, DOPAC and HVA were high in light hours and low in dark hours of the LD illumination cycle. In retinas of chicks kept under DD, the content of DA, DOPAC and HVA oscillated in a rhythmic manner for 2 days, with higher values during the subjective light phase than during the subjective dark phase. The amplitudes of the observed oscillations markedly and progressively declined compared with the amplitudes recorded under the LD cycle. In retinas of chicks kept under LL conditions, levels of DA, DOPAC and HVA were similar to those found during the light phase of the LD cycle. Changes in the retinal contents of DA and HVA did not exhibit pronounced daily oscillations, while on the first day of LL the retinal concentrations of DOPAC were significantly higher during the subjective light phase than during the subjective dark phase. Acute exposure of chicks to light during the dark phase of the LD cycle markedly increased DA and DOPAC content in the retina. In contrast, light deprivation during the day decreased the retinal concentrations of DA and DOPAC. It is suggested that of the two regulatory factors controlling the level and metabolism of DA in the retina of chick, i.e. light and biological clock, environmental lighting conditions seem to be of major importance, with light conveying a stimulatory signal for the retinal dopaminergic cells.     

Catecholamine content of the rat brain at different stages of experimental alcoholism

Changes in the noradrenaline (NA) content in the hypothalamus, dopamine (DA) and homovanillic acid (HVA) in the striatum were determined in rats after chronic alcohol administration. A single injection of alcohol (2.5 g/kg i.p.) provoked a 30% decrease in NA only in rats predisposed to ethanol intake. Voluntary intake of 15% ethanol for 10 days made the NA content return to normal, the 4-month use of ethanol did not change whereas the 8-month use reduced the NA content by 17%, DA by 31% and raised the content of HVA by 25%. Twenty-four hours after alcohol abstinence the HVA content dropped by 13%. It is concluded that the noradrenergic system is involved in the formation and development of alcohol motivation and that the dopaminergic system participates in the development of the physical dependence and abstinence.     

Retention mechanism of analytes in the solid-phase extraction process using molecularly imprinted polymers. Application to the extraction of triazines from complex matrices

The influence of sampling variables on the concentration of the dopamine metabolites 3-methoxytyramine (3MT), dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA) was examined in equine urine. A logarithmic transformation of the data for all horses gave distribution which approximated the normal distributions for each metabolite. The mean urinary concentration of 3 MT in horses was 214 ng/mL and the application of a threshold with a probability of 1 in 10,000 gave an actionable level of 4 microg/mL. Environmental variables were not forensically significant in determining the population distribution. HVA was not found to be a reliable indicator of dopamine or levodopa administration.     

Effects of kainic acid,quisqualic acid,and their antagonist,pCB-PzDA,on rat electrocorticograms and monoamine metabolite levels in rat striatum

The action of kainic acid (KA), quisqualic acid (QA), and 1-(4-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (pCB-PzDA) was investigated in the central nervous system of male Sprague Dawley rats. Intracerebroventricularly injected KA and QA (100 nmol) induced spike discharges, and pCB-PzDA (100 nmol) suppressed electrocorticograms for one hour. pCB-PzDA enhanced the KA-induced spike discharges and inhibited those induced by QA. 2,3-Di-hydroxyphenylacetic acid(DOPAC) and homovanillic acid (HVA) levels were increased transiently by 10 nmol and continuously by 100 nmol of KA. KA dose-dependently increased 5-hydroxyindoleacetic acid (5-HIAA) levels 2 hours after administration. While 10 nmol of QA slightly increased the HVA level, 100 nmol of QA significantly increased DOPAC, HVA, and 5-HIAA levels. DOPAC and HVA levels were increased by 100 nmol of pCB-PzDA, although this agent inhibited KA-induced increases in DOPAC, HVA, and 5-HIAA levels. On the other hand, while pCB-PzDA first inhibited QA-induced increases in DOPAC, HVA and 5-HIAA levels for one hour, DOPAC and HVA levels thereafter increased additively. These findings suggest that pCB-PzDA may act not only as a NMDA antagonist, but that it may also act directly on dopaminergic neurons.     

Correlations between aminergic metabolites simultaneously obtained from human CSF and brain

Brain and cerebrospinal fluid (CSF) levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were simultaneously measured in 48 individuals at autopsy. Concentrations of 5-HIAA and HVA in the cerebral cortex were positively correlated with their levels in the CSF for the same individual. Additionally a positive correlation was observed between postmortem CSF levels of 5-HIAA and HVA and a significant concentration gradient for both metabolites was observed in serial fractions of CSF. These findings suggest that determinations of 5-HIAA and HVA in CSF from living individuals may reflect brain metabolite levels as well as the functional activity of these specific neuronal systems.